Course-made-good apparatus for sailboats

ABSTRACT

A sailboat measures and displays course-made-good information with the use of a gimbal-mounted magnetometer sensor for detecting the direction of the earth&#39;&#39;s magnetic field. The magnetically sensitive axis of the sensor is aligned with the earth&#39;&#39;s magnetic field when the boat is headed on a desired course, and the sensor is then locked in a fixed position relative to the boat, with the magnetometer thereafter producing a voltage which is proportional to the cosine of the angular deviation of the boat from the desired course. A voltage signal representing boat speed is coupled with the voltage from the magnetometer in a multiplier to produce a voltage proportional to the vector component of the boat speed in the direction of the desired course. The voltage from the magnetometer sensor is fed to a meter to display the angular deviation of the boat from the desired course, and the voltage from the multiplier is fed to a meter to display the boat&#39;&#39;s velocity vector component in the direction of the desired course.

United States Patent Pounder et al.

1151 3,685,352 1 Aug. 22, 1972 [54] COURSE-MADE-GOOD APPARATUS FORSAILBOATS Inventors: Edwin Pounder, Sierra Madre; John I R. Casani,Altadena, both of Calif.

lnc., Burbank,

[73] Assignee: Transdynamim,

Calif.

Filed: Dec. 2, 1970 Appl. No.: 94,278

[5 6] References Cited UNITED STATES PATENTS 3,141,725 7/1964 Gray..73/l78 X Primary ExaminerDonald O. Woodie] Attorney-Christie, Parker &Hale [57] ABSTRACT A sailboat measures and displays course-made-goodinformation with the use of a gimbal-mounted magnetometer sensor fordetecting the direction of 'the earths magnetic field. The magneticallysensitive axis of the sensor is aligned with the earths magnetic fieldwhen the boat is headed on a desired course, and the sensor is thenlocked in a fixed position relative to the boat, with the magnetometerthereafter producing a voltage which is proportional to the cosine ofthe angular deviation of the boat from the desired course. A voltagesignal representing boat speed is coupled with the voltage from themagnetometer in a multiplier to produce a voltage proportional to thevector component of the boat speed in the direction of the desiredcourse. The voltage from the magnetometer sensor is fed to a meter todisplay the angular deviation of the boat from the desired course, andthe voltage from the multiplier is fed to a meter to display the boatsvelocity vector component in the direction of the desired course.

PATENTED M22 1912 SHEET 3 BF 3 COURSE-MADE-GOOD APPARATUS FOR SAILBOATSBACKGROUND OF THE INVENTION This invention relates to apparatus fornavigating sailboats, and more particularly to a system that measuresand displays course-made-good information, such as course-made-goodspeed and course-madegood heading. Course-made-good speed is defined Igenerally as the vector component of boat velocity in the direction of adesired course, with course-madegood heading being the angular deviationof the boat from the desired course.

When a mark to be reached is upwind from a sailboat, the boat is sailedon two or more courses at angles to the true wind, or tacks, to reachthe mark. When a mark to be reached is downwind from the sailboat, theboat can be sailed with the wind to reach the mark. However, in mostcases the downwind mark can be reached in shorter time if the boat issailed on two or more tacks with the wind, because the sails provideincreased airfoil action when the boat sails at an angle to the wind.

In each of these cases, the boat reaches its mark in minimum time if aparticular course is chosen so that the vector component of the boatsvelocity parallel to the true wind is as large as possible.

When a mark to be reached is at a large angle relative to the true wind,the boat is generally sailed in the direction of the mark. However, insome cases the mark can be reached in minimum time if the boat is sailedon two or more courses relative to the mark. This occurs if theparticular course is chosen so that the vector component of the boatsvelocity toward the mark is a maximum.

Generally speaking, sailboats have not been equipped with a device tomeasure and display coursemade-good information such as the boatsvelocity vector component in the direction of a desired course, and theangular deviation of the boat from the desired course. Such a deviceappears to be expensive and complex to mechanize completely,particularly because the true wind speed and its direction cannot beobserved from the moving boat.

SUMMARY OF THE INVENTION This invention provides course-made-goodapparatus to measure and display the heading of a sailboat relative to adesired direction and the vector component of the boats velocity in thedesired direction. The invention overcomes the problems of the prior artby providing a device which can be set to remember the true winddirection from a point in time when it can be observed directly.

Briefly, one embodiment of the course-made-good apparatus comprises asteering compass for measuring the angle between a reference line on asailboat and a desired direction. The steering compass includes amovable magnetometer sensor for detecting the direction of a magneticreference point from a point on the boat. The position of the sensor isadjusted and set at a fixed angular reference position defining aninitial angle between the magnetic reference point and the referenceline on the boat. A magnetometer circuit responsive to the setting ofthe initial angle produces a signal representative of the angulardeviation of the direction. The apparatus includes a sensing device fora measuring the angle between a reference line on the boat and a desireddirection. Alignment means mounted on the boat cooperate with thesensing device to produce a reference measurement of the angle betweenthe desired direction and the reference point. Means responsive to themeasurement produced by the sensing device and the reference measurementproduces a heading signal representative of the angular deviation of thereference line on the boat from the desired direction. A speed signalrepresenting the actual speed of the boat is coupled with the positionsignal to means for producing a velocity vector signal representative ofcourse-made-good speed, i.e., the vector component of the boat velocityin the desired direction.

Preferably, the position signal is fed to a meter to monitor angulardeviations of the boat from its desired direction, and the velocityvector signal is fed to a meter to monitor course-made-good speed.

In a preferred form of the invention, the sensing device comprises agimbal-mounted magnetometer sensor having a magnetically sensitive axisfor detecting the direction of the earths magnetic field, and alignmentmeans for locking the sensor in a fixed angmlar reference positionrelative to the reference line on the boat. A magnetometer circuit iscoupled to the sensor for producing a voltage signal proportional to thecosine of the angle between the magnetically sensitive axis of thesensor and the direction of the earths magnetic field.

Thus, when the boat is headed in the direction of a mark on a desiredcourse, the sensor is aligned with the earth's magnetic field and lockedin position to establish the reference position of the boat. Thereafter,as the boat is sailed on a tack relative to the desired course, themagnetometer circuit produces a voltage proportional to the cosine ofthe boats angular deviation from the direction of the desired course. Avoltage signal having a magnitude proportional to boat speed is coupledwith the magnetometer voltage in a multiplier to produce a voltageproportional to the magnitude of the component of the boats velocityvector in the desired direction. Thus, as the boat is sailed to reachthe mark, velocity vector information is monitored as the boat issteered to determine the particular course that produces a maximumvelocity vector relative to the direction of the desired course. If theboat is then sailed on that particular course, it reaches the mark inthe shortest time.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features of theinvention are more fully set forth in the following detailed descriptionof the embodiment of the. invention which is presently preferred, suchdescription being presented with reference to the accompanying drawings,wherein:

FIG. 1 is a schematic diagram defining course-madegood speed of asailboat sailing on a tack into the wind;

FIG 2 is a schematic diagram showing a velocity characteristic of atypical sailboat;

FIG 3 is a schematic block diagram showing the course-made-goodapparatus of this invention;

FIG. 4 is an elevation view of a gimbal system for mounting themagnetometer sensor;

FIG. 5 is an elevation view taken on line 5-5 of FIG.

FIG. 6 is a plan elevation .view taken on line 66 of FIG. 4; and

FIG. 7 is a schematic block diagram steering compass of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, asailboat 10 is sailed on a tack or course representedby a line 12 whichheads in the direction of the boats lubber line (longitudinalcenterline). The tack is shown heading into the wind. The true wind isrepresented by the vector 14 having a magnitude T, the tack being at anangle y (hereafter referred to as the heading angle or course-made-goodheading) relative to the direction of the true wind. The boat sails fora mark X in the direction of the true wind. However, since the boatcannot sail directly into the wind, it sails along the tack 12 with aspeedrepresented by a vector 16 having a magnitude B. The apparent windvelocity observed from the boat is represented by a vector 18 having amagnitude U acting in a direction represented by the angle B relative tothe boat.

The vector component of the boat velocity directly into the wind isrepresented by a vector 20 having a magnitude W which equals thequantity B cos'y. As described above, the boat reaches a mark upwind inthe shortest time when the boat sails on a tack on which the magnitudeof the vector velocity W, i.e., course-madegood speed, is a maximum.

FIG. 2 represents a velocity characteristic for a typical sailboatshowing the maximum velocity which the boat can achieve through thewater when sailing on a given course relative to the true wind. Forexample, when the boat in FIG. 2 sails on a tack into the wind at anangle 3 relative to the true wind, the boat achieves a maximum velocityB represented by the vector 22. The vector 23 represents the component Wof the boats velocity vector in the direction of the true wind, i.e.,the boats course-made-good speed.

When the boat in FIG. 2 sails on a tack into the wind, course-made-goodspeed (relative to the direction of the true wind) is a maximum when theboat is headed on the tack 24 that produces a course-made-good speedrepresented by the vector 24A having a magnitude V Similarly, when theboat sails on a tack with the wind, the vector component of the boatsvelocity relative to the direction of the true wind is a maximum whenthe boat is headed on the tack 26 that produces a course-made-good speedrepresented by the vector 263 having a magnitude V If the boat sailsdownwind without tacking, FIG. 2 shows that the boats coursemade-goodspeed is less than V,,.

If a mark X to be reached is at a large angle relative to the true wind,as shown in FIG. 2, the boat can achieve a velocity V in the directionof the mark. However, the velocity characteristic of FIG. 2 shows thatif the boat sails on a tack 28, it reaches a courseshowing the made-goodspeed vV toward the mark which can be largerthan velocity V,;.

The course-made-good speed characteristic is generally different foreach boat, and the characteristic is dependent generally upon the shapeof the hull and the type of rigging used on the boat. Furthermore, thecharacteristic for the same boat changes with time depending upon suchfactors as changes in rigging, sea conditions, and the degree of hullfouling.

This invention is based on the recognition that a device to measure anddisplay course-made-good information permits a skipper to select theparticular tack that produces a maximum velocity component in thedirection of a desired course. Course-made-good information is generallynot available because the true wind speed and its direction cannot beobserved from the moving boat. When the boat is moving, the boats apgatemagnetometer having a manually adjustable sensor 30 in the form of anelongated cylindrical rod with a longitudinal axis that senses thedirection of the earths magnetic field. A winding (not shown) disposedabout an intermediate portion of the sensor 30 is connected to aconventional flux gate magnetometer circuit, or flux gate electronics,represented generally by the block 32.

The operation of the magnetometer is well known. The magnetometercircuit 32 causes an alternating current to flow in the magnetometerwinding to thereby produce in the sensor 30 an alternating flux of thesame frequency. When the sensor is placed in a magnetic field, the fieldproduces a magnetic flux in the sensor that changes the magnitude of thealternating current through its winding. The change in current isamplified and converted to a voltage signal 34 that gives adirectmeasurement of the component of the magnetic field falling in thedirection of the axis of the sensor. Thus, the voltage signal 34 has amagnitude equal to a constant voltage times the cosine of the angle 0(see FIG. 1 which is the angle between the sensitive axis of the sensor30 and the direction of the earths magnetic field. Thus, voltage signal34 has a maximum magnitude when the sensor is aligned with the earthsmagnetic field (magnetic north), and the voltage falls off as the sensorturns away from the magnetic field. When the sensor is at a right anglerelative to the earth's magnetic field, e.g., magnetic east, the voltageis zero.

Voltage signal 34 is fed to a heading meter or course deviationindicator 35 having a scale that displays the voltage signal 34 as areading of the angle 0 between the magnetically sensitive axis of thesensor 30 and the direction of the earths magnetic field. Thus, when thesensor is aligned with the earths magnetic field, the magnitude of thevoltage 34 is a maximum, and the scale on the heading meter 35 reads 0.When the sensor is aligned with the earth 5 magnetic field but turned180 away from the magnetic north, the voltage 34 is also a maximum, butof opposite phase, so that the meter 35 reads 180. When the sensor isturned at a right angle from the earths magnetic field, the magnitude ofthe voltage 34 is zero, and the meter 35 reads A power cable (not shown)connects the heading meter to a 12 volt DC. power supply. A separatecable (not shown) connects the heading indicator to the magnetometercircuitry 32.

A gimbal system 36 mounted in a fixed position on the boat has an innergimbal ring 38 that mounts the sensor 30 to stabilize the motion of thesensor in the horizontal plane. Thus, the sensor remains in a horizontalposition independently of the pitching or rolling motion of the boatinduced by wave action and the like.

The construction and operation of the gimbal system 36 is bestunderstood by referring to FIGS. 4 through 6 which show a gimbal casing40 mounted in a fixed position to boat 42. The interior lower portion ofthe casing has an upwardly opening spherically curved surface 44 in theform of a cup. Gimbal rings 46 are mounted at the top of the casing 40above surface 44. The inner gimbal ring 38 mounts a pendulum 47 formedby an upright elongated pendulous shaft 48 that supports at its bottom aweight 50 having a spherically curved lower surface 52 which is closelyspaced from spherical surface 44. In use, the gimbals permit thependulum to pivot about the transverse axes at 53 so that the shaft 48constantly maintains a fixed vertical orientation as the casing moveswith the boat due to wave action. A puddle of damping oil 54 in the gap55 between the bottom of the weight 50 and upper surface 44 providesdamping for the motion of the pendulum. The damping force provided bythe oil is related to the viscosity of the oil, the mass of thependulum, and the width of gap 55.

The magnetometer sensor 30, which comprises a cylindrical rod, iscarried within an outwardly opening bore 56 formed in the pendulumweight 50. The entire device is made of a nonmagnetic material.

An elongated sleeve 60 fitted over an upper portion of the pendulumshaft above the gimbals carries a circular support plate 62. The sleevemaintains the support plate in a fixed position aligned with the lubberline of the boat while the pendulum shaft ,is free to rotate relative tothe sleeve. The support plate carries a compass rose card 64. A knob 66fastenedto the top of pendulum shaft 48 carries a pointer 68. In use,the knob is turned to rotate the pendulum shaft so as to align themagnetometer sensor 30 with the earth s magnetic field. The pointerturns with the shaft to indicate the position of the magnetometer sensorrelative to the lubber line of the boat. When the sensor is properlyaligned, the pendulum shaft is locked in a fixed position relative tothe lubber line by a friction device such as a clutch (not shown).

The windings on the magnetometer sensor 30 are coupled to an output leadwire 72 which leads from the bore 56 in weight 50 upwardly to be woundon the pendulum shaft. The lead wire is then secured to the bottom ofthe gimbal platform, and extended outside the casing for connection tothe module (not shown) that houses the flux gate circuitry shown at 32in FIG. 3. An elongated downwardly extending arm 74 is secured to thebottom of the gimbal platfonn by a pivot pin 76. A stop pin 78 isfastened to the pendulum shaft adjacent to the lower portion of the arm,and as the pendulum shaft rotates relative to the arm 74 the stop pin 78abuts against either side of the arm 74, depending upon the direction ofrotation, to limit further rotation of the pendulum shaft relative tothe casing. Rotation of the pendulum shaft is limited to prevent thelead wire 72 from breaking'in the event it is twisted too tightly on thependulum shaft. The arm 74 pivots about pin 76 through an arc of about20 in either direction after contacting the stop pin, so that the shaftcan be rotated through about 400 relative to the casing to provide aslight overlap in either direction of rotation.

In use, the magnetometer sensor 30 references the direction of a desiredcourse. When the boat is initially headed in the desired direction, themagnetometer sensor is immediately aligned with the earths magneticfield by turning the knob 66 until the meter 35 reads 0, indicating thatthe voltage signal 34 from the magnetometer is a maximum. Theabove-described friction device is then applied to preventrclative'movement between the sensor axis and the lubber line of theboat. Thereafter, the sensor remains stable in the horizontal plane andaligned at a fixed angle a (see FIG. I) relative to the lubber line ofthe boat. Thus, as the boat is steered at an angle away from the desiredcourse, the angle 0 between the sensor axis and the magnetic northchanges accordingly; i.e., the angle 6 continually measures the headingangle y. The output voltage from the magnetometer decreases inproportion to the cosine of the angle 0 between the boat and the desiredcourse, and the meter 35 indicates the magnitude of the angle 0.

The component of the boat velocity in the direction of the desiredcourse is measured by coupling the voltage signal 34 to a full-waverectifier circuit 80. The rectifier circuit produces an output voltagesignal 82 which is positive during each one-half cycle when the voltage34 is a negative value, so that the voltage 82 is proportional to thecosine of the angle 0, but of positive phase. The actual speed of theboat in the water is measured by conventional means, such as by a meter:83 which produces a voltage signal 84 having a magnitude B proportionalto boat speed. Voltage signal 84 is coupled with voltage signal 82 to amultiplier circuit 86 which produces an output voltage signal 88 havinga magnitude proportional to the product of the boat speed and theabsolute value of the cosine of the angle 0. Voltage signal 88, whichhas a magnitude B lcos0| is a measure of course-made-good speed W B cos7 since the angle 3 equals the angle 6. Voltage signal 88 is coupled toa course-made-good meter 90 which displays course-made-good speed. Theheading meter 35 displays the angle 7.

In use, the apparatus shown in FIG. 3 provides a rapid determination ofthe course, or tack, to follow to reach a given mark in the shortesttime. For example, if a mark to be reached is upwind from the boat inthe direction of the true wind, the desired course, i.e., the directionof the true wind, is referenced by heading the boat in the direction ofthe true wind and then aligning the magnetometer sensor with themagnetic north. The direction of the true wind is easily sensed becausethe true wind and apparent wind vectors are parallel when the boat isheaded into the wind. The magnetic north can be sensed by turning theknob 66 to move sensor 30 until the heading meter 35 reads 0.

A more accurate way to align the sensor with the magnetic north is tofirst move it to a position at a right angle relative to the earthsmagnetic field so the heading meter 35 reads either plus or minus 90.The sensitivity of the cosine voltage signal 34 in the vicinity of plusor minus 90 is substantially greater than it is near This permits asubstantially more accurate initial alignment of the magnetometersensor. After the sensor is aligned at a right angle from the magneticnorth, the position of the sensor is then turned 90, using the compassrose card 64 as a guide. Thus, the sensor is accurately aligned with themagnetic north. The previously described friction device is then appliedto lock the sensor in its'reference position.

Thereafter, the boat is steered to determine the tack into the windwhich produces a maximum reading on course-made-good meter 90. Thereading on heading meter 35 indicates the heading of the boat relativeto the direction of the true wind. When the time comes to change course,the boat is turned through an arc of substantially 90, using the meter35 as a guide, and the meter 90 is then monitored to determine thecourse which again produces the maximum velocity in the direction of thetrue wind. Tacking back and forth in this manner eventually permits theboat to reach the upwind mark in minimum time.

A similar procedure is followed to maximize coursemade-good speed whensailing with the wind.

When sailing for a mark at a large angle from the wind, for example, themagnetometer sensor is aligned with the magnetic north when the boat isheaded in the direction of the mark. Thereafter, the meter 35 measuresthe deviation of the boat from the desired rightangle course, and themeter 90 measures course-madegood velocity for determining whether aslightly different course will maximize the component of the boatsvelocity in the direction of the mark.

As discussed above, the voltage signal 34 from the magnetometer isrepresentative of the cosine of the angular deviation of the lubber lineof the boat from the boats desired direction. The cosine function is theinherent output of the magnetometer, and this feature is especiallyadvantageous in the present system because it eliminates the need for amechanism, such as an angle resolver, for deriving the cosine function.This permits the course-made-good speed measuring system of thisinvention to be implemented at a reasonable cost to most sailboatowners.

As previously explained, the combination of the magnetometer and thecourse deviation indicator 35 providesa steering compass for measuringthe angular deviation of the boat from a desired heading. The axis ofthe magnetometer sensor is simply aligned with the magnetic north whenthe boat is parallel to the desired heading (i.e., the angle between thesensor axis and magnetic north is 0). Thereafter, as the boat deviatesfrom the desired heading, the magnetometer produces a voltage signalwhich is proportional to the cosine of the boats angular deviation. Aspreviously explained, the sensitivity of the cosine function issubstantially greater in the vicinity of plus or minus 90 than it isnear 0. Thus, when the axis of the magnetometer sensor is aligned withmagnetic north to initially reference the boats desired heading, smallangular deviations from the desired heading are difficult to observebecause of the low sensitivity of the cosine function near 0.

FIG. 7 shows a magnetometer steering compass which produces an accuratemeasurement of small angular deviations of the boat from a selectedheading. In this system, when the boat is headed on its desired coursethe magnetometer sensor 30 is positioned at a angle from magnetic northwith the aid of the compass rose card 64, so that no output voltagesignal is generated by the magnetometer circuitry 32 when the card isoriented toward magnetic north. In this case, the axis of themagnetometer sensor is pointing toward magnetic east. When the selectedcourse is followed exactly, the voltage signal 34 from the magnetometerwill be zero since the sensor axis is oriented 90 from magnetic north.Any angular deviation 8 from the selected course will produce amagnetometer voltage signal 34 proportional to the sine of the angulardeviation 8. This voltage signal is transmitted to a course deviationindicator 92 which translates the signal into the angle of deviation 5from the selected course. The course'deviation indicator contains a dialface marked off in degrees from 90 to 0 to +90. The dial scale is linearwith the sine of the angular deviation 8. This effectively amplifiessmall angular deviations and allows fine steering of the boat. A pointer94 swings right or left of 0 to indicate the right or left deviationfrom the selected course.

In the magnetometer steering compass shown in FIG. 7 a cable (not shown)connects the course deviation indicator 92 to the flux gate circuitry.The steering compass may be built as a separate unit, with the flux gatecircuitry mounted on a separate circuit board. The course-made-goodspeed measuring system, which includes rectifier 80, the boat speedmeasuring device, multiplier 86, and course-made-good indicator 90, mayalso be constructed as a separate unit and mounted on a separate circuitboard. The steering compass may be used by itself to measure boatdeviation from a selected course, or it may be coupled to thecourse-made-good speed measuring system by means of a cable (not shown)to separately measure boat deviation and course-made-good speed.

The course-made-good apparatus of this invention is particularly usefulas a means for establishing a continuous record of the boatsperformance. The apparatus is also useful in providing a comparativemeasurement of the performance of various riggings.

The present invention has been described in the context of the preferredmeans for carrying out the invention, and it is understood that variousfeatures of the preferred embodiment can be modified without departingfrom the scope of the invention. For example, a different type ofmagnetometer than the flux gate magnetometer can be used to sense thedirection of the earths magnetic field. Furthermore, other means can beused to sense the direction of a fixed reference point. For example, acompass can be used to sense magnetic north, and the compass card can beadapted to drive a cosine potentiometer to measure the deviation of theboat from the desired course. A gyroscope can be used to establish aninertial reference point. Moreover, the phase of the voltage signal 34from the magnetometer circuitry is rectified to simplify converting thevoltage to the scale reading on meter 90. However, other means can beused for converting the voltage to a scale reading of course-made-goodspeed.

We claim:

l. Course-made-good apparatus for detecting the heading of a sailboatthat produces the maximum component of boat velocity in a desireddirection, the apparatus comprising:

a. means for sensing the direction of a reference point from a point onthe boat so as to produce a continuous measurement representative of theangle between the reference point and a reference line on the boat;

b. adjustable alignment means on the boat to cooperate with the sensingmeans to produce a reference measurement of the angle between thedesired direction of the boat and the reference point;

. means responsive to the instantaneous magnitude of the referencemeasurement and the angle measured by the sensing means for producing acourse deviation signal representative of the angular deviation of thereference line on the boat from the desired direction of the boat;

. means for producing a speed signal representative of the instantaneousspeed of the boat; and

means responsive to the course deviation signal and speed signal forproducing a velocity vector signal representative of the vectorcomponent of boat speed in the desired direction.

2. Apparatus according to claim 1 including'means responsive to thevelocity vector signal for monitoring the vector component of the boatspeed in the desired direction.

3. Apparatus according to claim 1 wherein the sensing means includes amagnetometer sensor for sensing the direction of the earths magneticfield; and wherein the alignment means includes means for maintainingthe axis of the sensor in a fixed position relative to the referenceline on the boat, whereby the sensor may be initially aligned with theearths magnetic field when the boat is headed on the desired course toproduce the reference measurement.

4. Apparatus according to claim 3 wherein the means for producing thecourse deviation signal includes magnetometer circuit means coupled tothe magnetometer sensor for producing a voltage proportional to thecosine of the angle between the axis of the sensor and the earth 5magnetic field.

5. For use with a sailboat, course-made-good apparatus for detecting theheading of a sailboat that will produce the maximum component of boatvelocity in a selected direction, the apparatus comprising:

a. magnetometer means including a movable sensing element for detectingthe direction of a magnetic reference point from a point on the boat;

. means for adjusting the position of the sensing element and settingthe element at a fixed reference position relative to a reference lineon the boat defining an initial angle between the magnetic referencepoint and the reference line on the boat when the boat is headed in theselected direction;

means coupled to the sensing element and responsive to the setting ofthe initial angle for producing a heading signal representative of thecosine of the angular deviation of the sensing element from itsreference position;

means for producing a speed signal representative of boat speed; and

e. means responsive to the heading signal and the speed signal forproducing a velocity vector signal representative of the vectorcomponent of boat speed in the selected direction.

6. Apparatus according to claim 5 including means responsive to thevelocity vector signal for monitoring the vector component of boat speedin the selected direction.

7. Apparatus according to claim 5 wherein the means for maintaining thesensing element in a fixed position includes a gimbal system fixed tothe boat and having a stable gimbal element for mounting themagnetometer sensing element to stabilize the motion of the sensingelement in the horizontal plane.

8. Apparatus according to claim 7 wherein the means for maintaining thesensing element in a fixed position further includes means for movingthe sensing element relative to the boat, and releasable locking meansfor maintaining the sensing element in a fixed position relative to theboat.

9. Apparatus according to claim 8 wherein the means for producing thevelocity vector signal includes multiplier means for producing an outputsignal representing the product of the magnitude of the boat speed andheading signals.

10. Apparatus according to claim 9 wherein the means for producing thevelocity vector signal further includes rectifier means for producing asignal representing the absolute value of the magnitude of the headingsignal.

11. Apparatus according to claim 10 including means responsive to theheading signal for monitoring the angular deviation of the boat from thedesired direction.

12. A method of detecting the heading of a sailboat that produces themaximum component of boat velocity in a desired direction, the methodcomprising:

a. sensing the direction of a fixed reference point from a point on theboat to continuously produce a sensed measurement representative of theangle between the fixed reference point and a reference line on theboat;

b. producing a reference measurement of the angle between the desireddirection of the boat and the fixed reference point;

c. responding to the reference measurement and the sensed measurement toproduce a course deviation signal representative of the angulardeviation of the reference line on the boat from the desired directionof the boat;

d. producing a speed signal representative of the instantaneous speed ofthe boat; and

e. combining the course deviation signal and the speed signal to producea velocity vector signal representative of the vector component of boatspeed in the desired direction.

13. The method according to claim 12 including monitoring the velocityvector signal.

14. The method according to claim 16 in which (a) a sensing devicesenses the direction of the reference point and generates an outputrepresentative of the angle between the reference point and thereference line on the boat, (b) the reference measurement is produced bypositioning the sensing device with respect to the fixed reference pointso that it generates reference line and the desired direction.

15. The method according to claim 14 including multiplying the coursedeviation signal and speed signal to produce the velocity vector signal.

J UNHTEU STATES PATENT UFFECE (JERTIFECATE 0F RRECTEON Patent NO- N0 26M, 2%? mAngusii2 l9lL Inventor(s) It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

IN THE CLAIMS:

.Column 10, line 61, after the word claim, change "16" to --l2-- Signedand sealed this 9th day of January 1973.,

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. Course-made-good apparatus for detecting the heading of a sailboatthat produces the maximum component of boat velocity in a desireddirection, the apparatus comprising: a. means for sensing the directionof a reference point from a point on the boat so as to produce acontinuous measurement representative of the angle between the referencepoint and a reference line on the boat; b. adjustable alignment means onthe boat to cooperate with the sensing means to produce a referencemeasurement of the angle between the desired direction of the boat andthe reference point; c. means responsive to the instantaneous magnitudeof the reference measurement and the angle measured by the sensing meansfor producing a course deviation signal representative of the angulardeviation of the reference line on the boat from the desired directionof the boat; d. means for producing a speed signal representative of theinstantaneous speed of the boat; and e. means responsive to the coursedeviation signal and speed signal for producing a velocity vector signalrepresentative of the vector component of boat speed in the desireddirection.
 2. Apparatus according to claim 1 including means responsiveto the velocity vector signal for monitoring the vector component of theboat speed in the desired direction.
 3. Apparatus according to claim 1wherein the sensing means includes a magnetometer sensor for sensing thedirection of the earth''s magnetic field; and wherein the alignmentmeans includes means for maintaining the axis of the sensor in a fixedposition relative to the reference line on the boat, whereby the sensormay be initially aligned with the earth''s magnetic field when the boatis headed on the desired course to produce the reference measurement. 4.Apparatus according to claim 3 wherein the means for producing thecourse deviation signal includes magnetometer circuit means coupled tothe magnetometer sensor for producing a voltage proportional to thecosine of the angle between the axis of the sensor and the earth''smagnetic field.
 5. For use with a sailboat, course-made-good apparatusfor detecting the heading of a sailboat that will produce the maximumcomponent of boat velocity in a selected direction, the apparatuscomprising: a. magnetometer means including a movable sensing elementfor detecting the direction of a magnetic reference point from a pointon the boat; b. means for adjusting the position of the sensing elementand setting the element at a fixed reference position relative to areference line on the boat defining an initial angle between themagnetic reference point and the reference line on the boat when theboat is headed in the selected direction; c. means coupled to thesensing element and responsive to the setting of the initial angle forproducing a heading signal representative of the cosine of the angulardeviation of the sensing element from its reference position; d. meansfor producing a speed signal representative of boat speed; and e. meansresponsive to the heading signal and the speed signal for producing avelocity vector signal representative of the vector component of boatspeed in the selected direction.
 6. Apparatus according to claim 5including means responsive to the velocity vector signal for monitoringthe vector component of boat speed in the selected direction. 7.Apparatus aCcording to claim 5 wherein the means for maintaining thesensing element in a fixed position includes a gimbal system fixed tothe boat and having a stable gimbal element for mounting themagnetometer sensing element to stabilize the motion of the sensingelement in the horizontal plane.
 8. Apparatus according to claim 7wherein the means for maintaining the sensing element in a fixedposition further includes means for moving the sensing element relativeto the boat, and releasable locking means for maintaining the sensingelement in a fixed position relative to the boat.
 9. Apparatus accordingto claim 8 wherein the means for producing the velocity vector signalincludes multiplier means for producing an output signal representingthe product of the magnitude of the boat speed and heading signals. 10.Apparatus according to claim 9 wherein the means for producing thevelocity vector signal further includes rectifier means for producing asignal representing the absolute value of the magnitude of the headingsignal.
 11. Apparatus according to claim 10 including means responsiveto the heading signal for monitoring the angular deviation of the boatfrom the desired direction.
 12. A method of detecting the heading of asailboat that produces the maximum component of boat velocity in adesired direction, the method comprising: a. sensing the direction of afixed reference point from a point on the boat to continuously produce asensed measurement representative of the angle between the fixedreference point and a reference line on the boat; b. producing areference measurement of the angle between the desired direction of theboat and the fixed reference point; c. responding to the referencemeasurement and the sensed measurement to produce a course deviationsignal representative of the angular deviation of the reference line onthe boat from the desired direction of the boat; d. producing a speedsignal representative of the instantaneous speed of the boat; and e.combining the course deviation signal and the speed signal to produce avelocity vector signal representative of the vector component of boatspeed in the desired direction.
 13. The method according to claim 12including monitoring the velocity vector signal.
 14. The methodaccording to claim 12 in which (a) a sensing device senses the directionof the reference point and generates an output representative of theangle between the reference point and the reference line on the boat,(b) the reference measurement is produced by positioning the sensingdevice with respect to the fixed reference point so that it generates agiven output when the boat is headed in the desired direction, and (c)the output of the sensing device varies as the reference line on theboat deviates from the desired direction of the boat, the output beingrepresentative of the angular deviation between the reference line andthe desired direction.
 15. The method according to claim 14 includingmultiplying the course deviation signal and speed signal to produce thevelocity vector signal.